Lifts have long been utilized for elevating heavy objects for any of a large variety of purposes. One potential hazard associated with any type of lift is that the same will inadvertently descend as a result of malfunction or human error. If a person or an object is under the lift at such a time, injury to the person or damage to the object are likely to occur, particularly when the lift is bearing a load.
One common form of a lift is that utilized for vehicle repair. Such lifts are commonly found in service stations, the service departments of vehicle dealers, and the places of business of vehicle mechanics. In recognition of the potential dangers posed by inadvertent descent of vehicular lifts, The Automotive Lift Institute of Indialantic Fla., at least as early as 1998, promulgated the following standard which in turn has been approved by The American National Standards Institute of New York, N.Y. The standard is as follows:
8.2.11 Load Holding Device                All automotive lifts except screw drive systems shall incorporate a mechanical device to prevent downward movement of more than 6″ (6 inches) after stopping motion. Function shall begin within twenty-four (24) inches of rise, and shall continue to the full rise position. If latches do not automatically reset after disengagement to prevent lowering the load, then the lifts shall incorporate a warning label at the point of latch operation and at the point of lift operation, that states that the latches do not automatically reset after lowering. The printed materials furnished with the lift shall incorporate the same warning.        
In practice, The Occupational Safety and Health Agency (OSHA) inspects places of vehicular lift use such as those identified above for compliance with the foregoing industry developed standard.
A particularly vexing difficulty occurs when lifts not meeting the foregoing standard are found. The owner/operator of the lift is then required to bring the lift into compliance, frequently at considerable expense.
For example, a common type of lift used for vehicular purposes is the well-known in-ground lift. Such lifts typically include a lift bed having a pair of spaced parallel rails engageable with the frame of a vehicle and connected by a cross brace typically referred to as the superstructure.
A hydraulic cylinder is located wholly within an excavation within the facility housing the lift and arranged so that its piston end is connected to the superstructure and moves the superstructure, and thus the lift bed, between a fully lowered position, resting on the underlying terrain and an elevated position, typically sufficiently high that an adult may walk, substantially unimpeded, beneath the lift.
Such lifts have also been typically provided with so called antirotation tubes which are cylindrical tubes connected to the superstructure in depending relation and located parallel to the lift cylinder. A tube is located in the excavation housing the lift cylinder and the antirotation tube is set to telescope into and out of such tube.
Of course, when excavation is required to remedy the deficiency, considerable expense is involved both in breaking the typical concrete floor and excavating below it, and then filling the excavation and replacing the floor once the upgrade is complete.
In one prior art structures, a single latch, and actuator therefor has been located on the antirotation tube so as to latch the lift and prevent descent more than a few inches below its uppermost position
Though the prior art design utilizing a single latch does allow replacement of a conventional antirotation tube with one provided with a single latch without the need for excavation or the like, the same structure does not provide for a limiting of inadvertent downward moment of more than 6″ for all lift position above 24 inches of rise.
The present invention is directed to overcoming the foregoing problems.